1. Field of the Invention
This invention relates to agglomeratesxe2x80x94in the form of shaped bodies or aggregatesxe2x80x94of substances for the preparation of an aqueous binder system, to their production and to their use.
Agglomerates in the context of the present invention are understood to be more or less porous collections of powder-form materials which are sufficiently coherent for practical application. If the agglomerates are irregularly shaped particles, i.e. do not have any regular geometric shape, but instead uneven or jagged surfaces, they are referred to as aggregates. If the agglomerates have a regular shape with flat or rounded surfaces, they are referred to as shaped bodies. The agglomerates are intended to consist of materials for the preparation of aqueous binder systems. An aqueous binder system in the context of the invention is understood to be a solution or dispersion used for bonding, strengthening or sealing. Specific examples are pastes, dispersion adhesives, primers for mineral substrates, etc. To obtain ready-to-use binders such as these, the dry agglomerates need only be dissolved or dispersed in water.
2. Discussion of Related Art
Agglomerates of the type in question are known. Thus, DE 31 03 338 describes a dry paste mix on powder-form cellulose ethers. Quick-dissolving granules between 100 and 600 xcexcm in size are produced from cellulose ethers with a particle size distribution of 90%  less than 200 xcexcm in the presence of added water in a granulator. Under the effect of the water added during granulation, the granules have a higher volume than before. Even after drying, the granules have a bulk density of only about 50% of the original powder mixture. This results in a higher consumption of packaging material which is undesirable. The granules can be formed in a press, for example to tablets 25 mm in diameter. These tablets are said to dissolve instantaneously after introduction into water and, after stirring just once for 5 seconds, form a ready-to-use paste after 8 minutes. The tablets contain cellulose ethers, glyoxal, phosphoric acid and ethoxylated fatty alcohols. They may also contain a polymer dispersion powder. The disadvantage of tablets with this composition is that the ready-to-use paste is not free from lumps which, on the outside, are gel-like but, on the inside, are still completely dry. These lumps dissolve very slowly even after vigorous stirring or after waiting for long periods.
This problem of lump formation is discussed in DE 42 00 188 and is solved by the presence in the tabletxe2x80x94in addition to the water-soluble dry polymerxe2x80x94of a product which reacts in the presence of water and releases a gas in the process. The product in question is preferably a dry acid component and a carbonate or bicarbonate. In addition, it is recommended to add other substances for disintegrating the tablets, for example starch, superabsorbers, silica and talcum. A superabsorber is described as a cellulose ether crosslinked in such a way that it is insoluble in water and is capable of absorbing around 50 times its weight of deionized water. The disadvantage of this solution is that all the substances used must have only a very low water content because otherwise premature gas generation occurs during storage of the adhesive tablets. In order to obtain the necessary disintegrating effect for the tablets, around 30 to 50% of the tablets consist of salts. This high electrolyte content leads to an up to 30% lower viscosity by comparison with electrolyte-free adhesive compositions which this considerably reduces the xe2x80x9cmileagexe2x80x9d of the paste.
Tablets of the type in questionxe2x80x94with or without superabsorbersxe2x80x94have at least one of the following disadvantages:
production under rigorous dry conditions only,
inadequate tablet strength,
lack of stability in storage through sensitivity to moisture and
small lumps which only disappear after 30 minutes.
In DE 197 02 026, these disadvantages are avoided by producing the shaped bodies under moderate conditions so that even the edges of the shaped body are porous. To this end, the powder-form materials for preparing the paste are formed with 5 to 40% by weight of water into blanks which are strengthened by gentle heating, more particularly by exposure to microwaves. The disadvantage of this solution lies in the expense of using microwaves.
Against the background of this prior art, the problem addressed by the present invention was to avoid the disadvantages mentioned above and, in particular, to provide an agglomerate of substances for the preparation of an aqueous binder system which, even after storage for several months, would dissolve in water without any lumps after gentle stirring for the usual time of at most about 15 minutes and would produce substantially the same viscosity as the corresponding powder without any disintegrators.